Ligand binding properties of hemoglobins provide a basis for understanding cooperative and regulatory functions of allosteric proteins. Precise analysis of ligand binding curves, of heats of reaction, of linked proton effects, and of the influence of allosteric effectors is required. We intend to continue application of available and new methods in collaborative efforts to better understand the unique functional feature exhibited in selected hemoglobins and respiratory proteins. The binding properties of hemoglobins are mediated by their state of aggregation. Oxygen binding curves of concentrated solutions of HbS are needed to determine the effect of ligand linked aggregation. Interaction energies in the tetrameric forms of HbA and beta 4 can be assessed from heats of dilution studies. Binding curve studies are proposed for minor components (Ala, Alb, Alc, and A2) of HbA. Special microcalorimetric, electrophoretic, and binding curve techniques are proposed to characterize properties for limited quantities of samples. A comparative study of the functional properties of hemoglobins (HbA, HbS, Trout Hb) and respiratory proteins (hemocyanins, erythrocruorins) is proposed to broaden our understanding of the allosteric concept.